The purpose of this research is to understand the mechanism for increases in dental caries observed in man and experimental animals ingesting elevated quantities of the trace mineral selenium. In order to accomplish the above, we will measure the influence of different dosages of inorganic selenium (sodium selenite) and organic selenium (seleno-methionine) on the development of experimental dental caries in the white rat. We also plan to measure the levels of selenium in successive layers of enamel from human teeth in order to determine how selenium is taken up into human teeth (i.e. before or after tooth development). Such studies should help to determine the relative significance of selenium in the total susceptibility of enamel to dental caries.